Actinomycin D can be reduced enzymatically, chemically or electrochemically to a free radical state. Absorption and electron spin resonance spectra of actinomycin D and its phenoxazone analogs show that a one electron reduction produces the free radical and yields hyperfine structure for prediction of electron residency. The flavoenzymes, NADPH cytochrome P-450 reductase, xanthine oxidase, NADPH cytochrome C reductase, nitrate reductase, and lipoamide dehydrogenase catalyze reductive cleavage of the anthracyclines and free radical formation. Human daunorubicin pH 6.0 reductase is purified and classified as a ketone reductase.